1. Field of the Invention
The present invention relates to a printer, and more particularly, to a printer capable of variably controlling a Revolution Per Minute (RPM) of a cooling-fan depending on an operation mode of a printing unit and a method of driving the cooling fan of the printer.
2. Description of the Related Art
As shown in FIG. 1, a conventional printer employing an electrophotographic developing method includes a pick-up roller 101, a charging roller 103, an organic photoconductive (OPC) drum 105, a transfer roller 107, a developing roller 109, a supplying roller 111, a fusing device 113, and a light exposure device 115, to print a predetermined image data on a sheet of printing paper 117. That is, the charging roller 103 electrically charged with a high charging voltage rotates to electrically and uniformly charge a photosensitive material coated along an external circumference of the organic photoconductive drum 105, and light emitted from the light exposure device 115 forms an electrostatic latent image on a surface of the electrically charged organic photoconductive drum 105. An electric potential difference then occurs between the supplying roller 111 supplied with a supplying voltage, e.g., a higher voltage, and the developing roller 109 supplied with a developing voltage, e.g., a lower voltage, than that of the supplying roller 111, thereby moving a negative charge from the supplying roller 111 to the developing roller 109. Accordingly, toner supplied from the developing roller 109 is coated on the electrostatic latent image formed on the surface of the organic photoconductive drum 105 to thus form a visible image. The transfer roller 107 of a transfer voltage, e.g., another higher voltage, transfers the visible image formed with the toner coated on the surface of the organic photoconductive drum 105 to the printing paper 117. A pre-transfer lamp (PTL) 123 emits light having a predetermined wavelength onto the organic photoconductive drum 105 to decrease an electric potential of the toner coated on the organic photoconductive drum 105. As a result, a binding force of the toner with respect to the organic photoconductive drum 105 decreases to thus improve a transfer efficiency of the toner from the organic photoconductive drum 105 to the printing paper 117. The visible image transferred to the printing paper 117 is settled down on the printing paper 117 due to a high temperature and a high pressure of a heating roller 119 and a compressing roller 121, which are provided in the fusing device 113, and printing work is then finished.
At this point, the supplying voltage, the developing voltage, the transfer voltage, and the charging voltage as described above are kept continuously supplied to the supplying roller 111, the developing roller 109, the transfer roller 107, and the charging roller 103, respectively, until the printing work is finished. Also, the heating roller 119 of the fusing device 113 maintains in a turned-on state and a predetermined temperature until the printing work is finished. A cooling fan 125 generates air current to cool heat that occurs in the printer due to the heating roller 119 and the printing work.
FIG. 2 is a view showing power supply signals to be supplied to the cooling fan 340 corresponding to operation modes of the printer of FIG. 1 and RPMs of the cooling fan 340 corresponding to the power supply signals.
As shown in FIG. 2, the operation modes of the printer are a warming-up mode 201, a standby mode 202, a first printing mode 203, a second printing mode 205, and a sleep mode 207. When the printer is applied with an initial power, in the warming-up mode 201, the heating roller 119 is heated to a predetermined temperature, and the cooling fan 125 is supplied with a power, thereby switching the warming-up mode 201 to the standby mode 202. The standby mode 202 maintains the predetermined temperature of the heating roller 119 at a predetermined degree such that the printing work is performed within a very short period of time (for example, from 0.5 seconds to 3 seconds) from an input of a printing command. In the first printing mode 203, a series of printing operations are performed according to the input of the printing command, maintaining the temperature of the heating roller 119 at another predetermined degree higher than that of the standby mode 202. In the second printing mode 205, the printer performs printing on the printing paper 117 thicker than a general printing paper or printing on a special paper, such as an OHP film. In the second printing mode 205, the printer performs the printing with the temperature of the heating roller 119 being lower than that of the first printing mode 203 and higher than that of the standby mode 202 and with a printing speed being slower than that of the first printing mode 203. In the sleep mode 207, the printer maintains a power saving condition by blocking a power from being applied to the heating roller 119 when the printer does not receive the printing command for a predetermined period of time on the standby mode 202. At this time, the cooling fan 125 is continuously driven or a power to the cooling fan 125 is blocked after another predetermined period of time passes in the sleep mode 207.
Since in the printer employing an electrophotographic developing method as described above, the temperature of the developing roller 119 becomes different (variable) according to each operation mode of the printer, an inner temperature of the printer also varies. However, the cooling fan 125 is always driven at the same RPM regardless of the inner temperature of the printer as shown in FIG. 2, to discharge the heat of the heating roller 125 outwardly even in the early time of the warming-up mode 201. Accordingly, a warming-up time (from t0 to t1) to meet the condition of the standby mode 202 takes a longer time. Also, there occur problems of shortening a lifespan of the cooling fan 125 and an increased power consumption of the printer. Also, since the conventional printer drives the cooling fan 125 at the same RPM regardless of the printing speed on the printing mode, a higher printing speed of the printer causes an inside of the printer to be overheated.